SURFACE RECOVERY AND STRIPPING METHODS TO QUANTIFY PERCUTANEOUS-ABSORPTION OF CAFFEINE IN HUMANS

The percutaneous absorption of caffeine from two vehicles, an emulsion and an acetone solution, was quantified by in vivo techniques in huma ns. A surface recovery technique over a 6-h application and a strippin g method after a 30-min application were performed on the volar aspect of the forearm on 12 volunteers. Caffeine was assessed by HPLC. Two p hases were distinguished in the percutaneous absorption of caffeine: a higher filling up of the stratum corneum with the oil-in-water emulsi on than with the acetone solution, which was then followed by a steady -state flux corresponding to the penetration in the living tissues. Th e permeability constants (K(p)) with emulsion and acetone were 1.59 . 10(-4) and 9.53 . 10(-8) cm/h, respectively. The stripping method show ed concentrations of caffeine in stratum corneum that were five times higher with emulsion (212 ng/cm2) than with acetone (37 ng/cm2). With acetone as a vehicle, approximately 40% of caffeine of the cornified l ayer was found around the treated area. This sizeable lateral spread w ithin the stratum corneum was not observed with the emulsion.